hapFabia identifies short identity by descent (IBD) segments that are tagged by rare variants in large sequencing data. Two haplotypes are identical by descent (IBD) if they share a segment that both inherited from a common ancestor. Current IBD methods reliably detect IBD segments longer than 1 Mbp (mega basepairs). hapFabia detects IBD segments in the range of 10 kbp (kilo basepairs). Many cohort studies contain unrelated individuals which share only short IBD segments. New sequencing techniques provide rare variants which convey more information on IBD than common variants, because random minor allele sharing of rare variants is less likely than for common variants.